Two British scientists seeking permission to create cloned human embryos using cow eggs have renewed an old debate about these “chimeras,” which may offer a new embryonic stem cell source for research but are also a source of controversy.

Stem cell researchers Stephen Minger, director of the Stem Cell Biology Lab at King’s College London, and Lyle Armstrong, a researcher at the North East England Stem Cell Institute applied to the Human Fertilisation and Embryology Authority, the agency overseeing all British reproductive and embryo research, to carry out cloning experiments using human genetic material and cow eggs. The controversy surrounding the experiments has exploded on both sides of the Atlantic.

Do you object? If so, why? Does this seem like sacrilege? Or are you afraid where it might lead?

These scientists aren't trying to create fully formed creatures. The cell lines they might be able to create could reveal useful lessons about genetic regulation and interactions between different genetic variations that normally do not interact in nature. But this research sort of research will lead to the identification of compatibilities and incompatibilities between genes across species. That knowledge could some day be used to figure out how to make human compatible versions of genes from big cats, dogs, cows, monkeys, and many other species.

But why would we want to transfer genes from other species into humans? Some would do it to fulfill aesthetic desires. Someone might want a coat of fur made from the same genes as that beautiful coat of fur that their cat Fluffy has. Or how about a tail? Exotic dancers and prostitutes might find that the ability to look like female characters from the X-Men movies would boost their incomes by sizable amounts.

But transplantation of genes from other species into humans holds out the potential for very practical medical benefits as well. The Methuselah Foundation LysoSENS research initiative has as its goal to find genes in bacterial, molds, and other very small organisms that can be transferred into human cells to better break down trash that accumulates in cells as we age. Our own lysosomes contain lysozyme enzymes that break down junk. But over decades they encounter pieces of junk they can't break down and that junk accumulates in our cells and contributes to our aging. By isolating and studying lysozyme enzymes in other species the LysoSENS researchers hope to find enzymes we can transfer to humans with gene therapy to let us clean out our cells.